This invention is in the field of methods and systems for transmitting images or video over channels where there is a bandwidth limitation present, where the channel possibly is lossy or where latency is important. The general problem to solve is the transport of high-quality images or video from one point to another. Because of the bandwidth limitations of the channel used it may be necessary to tolerate some decrease in image or video quality, this is for instance the case when the image or video data is compressed in a lossy way before sending it over the channel. In that case the decompressed image or video sequence will be of lower quality than the original image or video sequence. Frequently used compression schemes are JPEG, JPEG2000, MPEG-2, . . . . Each of these compression schemes has its advantages and disadvantages related to compression ratio, complexity of the scheme, calculation power needed, introduced latency, . . . and the best compression scheme to use also typically depends on the contents of the image or video that is compressed. For example: a medical image would require another compression scheme for optimal quality and compression ratio than a clip-art picture. Especially for demanding applications such as medical imaging a general decrease in image quality might not be acceptable so the bandwidth limitations clearly are in conflict with the need for high quality of at least the medical image being transmitted.
In case the transmission channel has a significant bit-error-rate (if the channel introduces errors in the transmitted data) then the degradation of the image or video quality might be totally unacceptable. Especially the combination of bit errors and compressed data typically introduces large errors in the decompressed data stream. This problem is referred to as error resilience. One possible solution in case of channels with high bit-error-rate is to use error detection codes or error correcting codes (ECC). These codes allow for detecting and even correcting bit errors within certain limitations. Examples of error correcting codes are CRC (cyclic redundancy codes) and RS (Reed-Solomon codes).
Apart from possible quality degradation compression also adds some extra latency because it takes time to compress and to decompress the stream. In some applications latency is a big problem. This is in particular the case if the data traffic is bi-directional. This is for example the case if a server generates video sequences, this video data is transmitted to the client, and the client has the possibility to interact with the server (by moving a mouse pointer for instance). In that case a high latency will immediately be visible as slow response of the system: it will take an unacceptable long time before the result of an action (mouse movement for example) of the client will take effect.
Furthermore, the device that receives the image or video data will typically be a portable device and therefore will have a wireless interface to the server. This aspect of portability results in extra complication what concerns power consumption, signal integrity (varying signal quality and possible loss of connection with the server) and security aspects. Indeed, portable devices are normally battery powered and to reach a useful battery operation time it is required to minimize the power consumption as much as possible. This conflicts with the bandwidth limitations of typical transmission channels (Wifi 802.11.a/b/g/ . . . , DECT, ZigBee, UWB, . . . ): because of the low available bandwidth a high compression ratio is needed and this typically requires a complex compression scheme. The complexity of the compression scheme is directly related to power consumption, as extra calculations require additional power. Portable devices also suffer from varying signal quality. With Wifi for instance, moving the device only a few meters can result in only half the available bandwidth because of complex reflections and inference of the wireless signal. Worst case, the signal can even fade away completely (for a limited time). In such a situation it is of course not desired that the portable device cannot be used at that moment. Because the data is transmitted wirelessly it is easier for other people to receive the data. In case the data is confidential (such as medical images or patient data) this will need extra precautions such as encryption algorithms.